1. Field of the Invention
The present invention relates to winches and hoists used in aircraft and in particular, to cable hoist systems adapted for use in a helicopter to sense cable fouling, control the disposition of the cable with respect to the drum, and signal cockpit personnel that fouling has occurred.
2. Description of the Related Art
There are many ways in which a cable can be fouled at the cable drum. For example, cable used with winch drums can be fouled by parting of the cable, kinks in the cable or an excessive amount of slack in a standing portion of the cable. During reeling operations, the cable can become loosened on the drum and foul. A broken strand of wire from the cable will force successive layers of cable out of alignment with respect to the drum, thereby causing the cable to foul on the drum.
In helicopters, a cable is more susceptible to fouling due to the heavy vibrations which occur on the aircraft's fuselage. Exposure of the fuselage to the vibrations requires that the winch assembly and cable be particularly adapted to operate in the "choppy" environment caused during helicopter operations.
It is therefore especially important to be able to sense immediately when a cable has fouled to prevent irreparable damage to the cable and the winch, and harm to personnel in the immediate area if the cable should part. Just as important is that a cable foul sensor device be able to distinguish between the vibrations in the fuselage of the helicopter, and an actual cable foul which will adversely impact on cable operations.
Cable winding safety devices are known in the elevator and well drilling arts. For example, U.S. Pat. No. 641,242 to Sprague discloses a cable winding safety device having a bar which lies parallel with and close to the face of a cable drum so that the space between the cables will be considerably less than the height of the ridges of the drum with the thickness of the cables. When cables climb out of their groove, the bar is forced back to coact with a switch arm above the drum to open the switch and stop the drum.
U.S. Pat. No. 813,451 to Rohlfing et al discloses a safety device for hoisting mechanisms which is used to control or stop the main hoist of the motor when the hoisting limit has been reached. The device consists of a rocking lever disposed at an interior of the drum and from which a trip-pin extends to project out of the drum. A trip pawl is mounted to coact with the other end of a rocking lever and be forced to extend from the drum to contact a switch when the trip-pin has been forced downward against the rocking lever by the cable being wound around the drum and down upon the trip-pin.
U.S. Pat. No. 1,163,165 to Mueller discloses a safety device for elevators consisting of a flexible metal strip, wire or bar arranged in proximity to a cable drum and extending longitudinally along said drum and spaced therefrom. A loose or broken strand of cable will make contact with the safety device for an electro-responsive controlling device to trip the switch controlling the drum.
U.S. Pat. No. 2,019,512 to Stahl discloses a means for preventing reverse winding of a cable on a drum, which device consists of a latch lever having a land stop and a groove stop which ride along the cable and grooves of the drum to actuate a stop switch when the cable has been taken out from the drum, or when a sufficient amount of cable has been wound upon the drum.
U.S. Pat. No. 2,053,976 to Stahl discloses a detent means for cable drums consisting of a recess in the first turn of the guide groove of the drum and in which a detent lever is arranged to lie in the recess and is pivotally carried by means of a pivot pin secured to the body. When the last turn of cable has been unwound off the drum, further movement of the drum will cause the arm to signal all the cable has been unwound.
U.S. Pat. No. 2,489,913 to Logan discloses a hoist control mechanism consisting of a pair of rocker arms which coact with a roller and control cam on the drum to control movement of the drum.
U.S. Pat. No. 3,031,169 to Robinson et al discloses an apparatus for automatically controlling drilling, which consists of an auxiliary control unit operable by valve means to which a pressure line is connected. The auxiliary control unit senses movement of the drum.
U.S. Pat. No. 3,182,961 to Le Bus discloses a combined fleet angle compensator and braking apparatus consisting of an eccentric shaft along which a sheave guard member moves. A braking mechanism is spaced from the eccentric shaft and is provided with a braking plate member adapted to engage the outer periphery of the cable spooled on the drum in the braking position. Upon release of tension in the cable, the braking plate is moved into contact with the outer layer or wrap of cable upon pivotal movement of the arm 24 to prevent slack in the cable from fouling on the drum.
U.S. Pat. No. 3,994,476 to Van Genneup discloses an automatic arrangement for a windlass to prevent unwanted reverse rotation of such windlass. The device consists of a load sensing lever arm, with one end pivotally mounted to the housing and the other end extending to support a pulley for the windlass block and tackle. Brake pressure is applied when the sensing lever succumbs to a particular amount of downward force resulting from the load thereon.
U.S. Pat. No. 4,213,019 to Houp discloses an overhead door cable safety device consisting of a U-shaped monitoring arm disposed in a spaced relationship adjacent to a top of the cable wrapped around a cable drum. Movement of the monitoring arm upward against the biasing of springs closes a switch to signal that the cable has been disengaged, unraveled, or frayed.
U.S. Pat. No. 4,448,394 to LeMoine discloses a high low safety apparatus for drilling rigs consisting of a pair of longitudinally moveable stems at opposed sides of a cable drum, each of the stems having a hemispherical surface which are normally positioned spaced from the cable on the drum. Movement of the hemispherical surface of the stem moves a valve element to allow passage of air through the valve to stop actuation of the drum.
U.S. Pat. No. 5,335,895 to Sell discloses a sensing rope guide for a hoist drum consisting of a split steel ring joined at the top by a steel hinge and held together at the bottom by a spring and bolt which encircle at least a portion of the drum. Steel groove rollers are housed in pockets of the ring to contact a sensing valve. If travel over the ring along the hoist drum is impeded by resistance from a side pull acting on the retainer and arm, or resistance from some other cause acting at some other point on the ring, the groove rollers cam out to actuate the sensing valve and prevent further operation of the hoist in the same direction.
However, among the devices disclosed in the patents above, none are especially adapted for use in aircraft, such as helicopters, and the particular environmental conditions these machines operate in. The heavy vibration of a helicopter fuselage requires the need for a cable foul sensing device which is immediately responsive to a cable foul at the drum, yet will not inadvertently be tripped due to the heavy vibration that the cable drum and cable are exposed to.